Facsimile signaling system



Oct. 16, 1945. c. J. YOUNG 2,386,997

FACSIMILE S IGNALING SYSTEM Filed Dec. 8, 1943 3 Sheets-Sheet l Moo F40/0 ZWA/f/w/ffff l ATTORNEY Oct.16,A 1945. c. J. YOUNG FACSIMILE SIGNALING SYSTEM Filed Deo. 8, 1943 5 Sheets-Sheet 2 ATTORN EY Oct. 16, 1945. c. J. YOUNG FACSIMILE SIGNALING SYSTEM 3 Sheets-Shag?. 5

Filed Dec. 8, 1943 la" l INVENTOR (Pw/wi: J )6a/v6.

ATTORNEY be employed in modulated image signal.

`.Anotherobject of the .present invention is tov Patented Oct. 16, 1945 FACSIMILE SIGNALINGl SYSTEM Charles J. Young, Princeton, N. J., millier to Radio Corporation of America, a corporation of Delaware Application December s, 1943, sensi No. 513,373

1o claims. (Cl. ris- 6.6)

The present invention relates to facsimile signaling systems and more particularlyto a receiving and recording system for producing records in facsimile from a phase modulated carrier.

If a 'carrier is phase modulated with image signals representing a picture, object. or other subject matter, the shade of black is represented by a shift of carrier phase' of a given number of degrees from a zero position for each shade. Detection cannot be accomplished, as with a sound phase modulated signal, by an inertia detector which 'centers on the average frequency because the image signal has a zero frequency component. In facsimile work, it is necessary to provide means for representing or obtaining this zero frequency component at the receiver. Moreover. it is at times necessary to be able to hold a black or white condition at the recorder for relatively long periods, which can be done only if a fixed reference isprovided.

I n facsimile systems where faithful shade representations are to be made, a xed reference point for the zero 'phase state must be available at the receiver from which to effect the control. 'I'he present invention has for its principal aim that of providing for such a.y zero phase reference point in a way which will be more stable than can be provided by any ordinary oscillator.

To accomplish this, the synchronizing frequency usually required for facsimile transmission, is used to provide a zero phase reference point. Preferably, the synchronizing frequency to this manner is one which is transmitted over the communication circuit along with the image signals. This transmission may be a direct wireline transmission or transmission over a radio channel. Y

'I'he primaryobject of the present invention, therefore, is to provide a novel system for -producing improved facsimile records from a phase employ a synchronizing signal in a novel manner to provide a reference frequency for a facsimile recording operation. V

Still another object of the present invention is to operate a facsimile recorder in accordance with an image signal derived from a phase modulated carrier and a substantially constant reference frequency.

A still further object of the present invention is to provide a no vel methodof recording image Simals representing a picture,

the utilization of -a synchronizing signal as a reference frequency with which the phase of the image signal is constantly compared during the recording process.

Other objects of the invention will become apparent when the following 'specification and claims are read in connection with the accom-` panying drawings, wherein:

Fig. 1 shows schematically a. transmitting station for originating phase modulated image signais;

Fig. 2 shows schematically a facsimile receiving station which operates in accordance with the invention to record signals; f

Figs. 3 to 10 inclusive are explanatory diagrammatic' curves; and

Fig. l1 shows a slightly modified receiving station.

scanner orl the like indicated generally by reference character I0. This scanner may be of any desired type but, for purposes of illustration, is shown as comprising a copy holding drum I 2 and a facsimile signal generating scanning head I4 propelled axially along the drum by a lead screw I6. For slow speed scanning any suitablechange speed device Il may, if desired. be used to connect the drive shaft I8 of a driving motor 2i with the drive shaft 22 of the scanner. For example, gearing or a friction drive wheel may be employed. A gear and pinion combination 23 drives the lead screw I6 at the proper relative speed so that closely spaced helical scanning lines are obtained as the scanning head Il moves axially of the drum I2.

The motor 2l is preferably. a variable speed motor such as an induction motor and is connected to a suitable power source 2 8. The motor may be caused to operate at the desired definite scanning speed byemploying' the synchronizing arrangement disclosed in the copending application of Maurice Artzt, Serial No. 504,337, illed September 30, 1943, modified with respect to the transmission of the synchronizing signal as disclosed'hereinafter, if desired.

In this synchronizing arrangement, briefly, synchronization is Vaccomplished vby producing a square wave representative of the speed of the apparatus to be synchronized by means of an induction generator 28. 'I'his output is supplied to the hunting amplifier SI, andthe resulting wave'is compared with a square wave representative of the desired scanning speed which is representative of the output from a limiter amplifier 32, which has been energized by the output (multiplied, if desired) from aclosely controlled standard frequency source 33. These two waves, when beat Referring to Fig. 1, there is shown a facsimile beat frequency wave is employed to energize an electric brake 38 mechanically connected to the driving motor 2|, or to a moving part of the scanner I0. This synchronizing arrangement depends vfor its operation upon phase comparison of two control waves. One of these is the frequencyv produced by the generator 2B, when the scanner I8 is operated at desired scanning speed, which is compared with a wave of like frequency. Therefore, to produce the desired wave, a frequency multiplier 39 is frequently employed to change the frequency of the output, from the standard source 33 to that of the generator 28 so that vthe comparison can be made.

The signal output from the scanning head I4, which varies in value in accordance with the shades of black and white of the copy on the cylinder i2 as it is scanned is employed to phase modulate a suitable subcarrier derived from a frequency multiplier 42.- The multiplier 42 is connected to the standard frequency source 33 over conductors 45 so that the frequency thereof remains constant. The modulator 43 may be of any desired type which shifts the phase of the carrier output from the multiplier 42 in accordance with image signals from the pickup or scanning head I4. A suitable modulator for this into any desired communication channel such as a wire line or carrier channel. For purposes of illustration, the carried channel is shown as being provided Aby a modulator and radio transmitter d3.

The receiving'station 'shown on Fig. .2, which operates in accordance with the invention, corn-v prises a radio receiver 52 of any well known vtype which will demodulate the carrier from the modulator and radio transmitter d8. The output of the receiver 52, appearing inthe circuit 53,

is divided into its two original components by venience of illustration) may be an inductor generator like thegenerator 28, associated with the scanner |0. The synchronizing tone applied in Fig. 1 to the mixer 46 is separated by the tone signal separator or tuner 56 and is multiplied in a frequency multiplier 68. This frequency multiplied synchronizing tone is also applied to the frequency comparison device 64 over conductors li. 'The brake 60 is connected in series with a 10= suitable power source (not shown) connected at terminals 'I4 by way of conductors 'It and ll.

It will be seen from the foregoing that the recorder driving and synchronizing arrangement is similar to the driving and speed controlling arrangement for the scanner lll of Fig. 1 of the drawings.

.As pointed out previously, a definite reference frequency is fto be provided, in accordance with the invention, for deriving image signals suitable for the operation of the rerde'r 59. This is accomplished by using the output from the standard frequency source 88 at the transmitter which is multiplied in frequency by the frequency multiplier 68 after transmission and' separation. The wave shape of this frequency multiplied signal is modied to square wave form in a limiting amplier 'i9 and the phase modulated signal wave obtained by demodulation in the receiver 52, after separation by the high pass lter 54, is limited and squared in a limiting amplifier 82.

Figs. 3 to 6 of the drawings will be referred to in explaining the operation of the arrangement which is provided for` obtaining the derived signal. The curves of Figs. 3 to l0 are illustrative only and are not intended to represent exact values to scale, although the general wave form closely resembles that occurring in operation. In Fig. 3, the wave 84 represents the stable frequency which is obtained from the output of the frequency multiplier 68. The wave -83 represents the phase modulated subcarrier appearing in the input ofthe limiter amplier 82. Assuming that the scanner i8 and modulator 43 of Fig. 1 are so arranged that the. shade of black in the original copy is represented by a shift of the l carrier phase of' a different number of degrees any known means which may, for example, be a high pass lter 513 and a band pass filter or tuner 53. It will be understood that if wire line transmission is desired, the connection 51 at the transmitting station of Fig. 1 may be connected to the circuit 53 by a Wire line path. Also, if 68 is a modulator, the arrangement of` Fig. 11 will be used.

A facsimile recorder shown schematically at 59 may be of any kind such, for example, as the carbon paper recorder shown in my Patent No. Re. 20,152, granted on October 27, 1936, or alternatively, it may be oi the electro-chemical or photographic type Vwhich are each well known. The drive shaft t2 for the recorderor any other mechanically moving part is provided with a brake ou which may be similar to the brake 33 on the scanner i@ of Fig. i; A frequency comparing device 66, whichmay be similar to the limiting ampliers 3|, 32, and the network 3S of erator inthe recorder (while not shown for confrom zero position for each shade, the curve of Fig. 3 represents the phase relationship between Y the phase modulated subcarrier 36 and the stable frequency 86 when a mid-grey portion of the original copy is being scanned.

After passing through the limiting amplifiers 'i9 and 32. the waves 84 and 8S respectively are as indicated by reference characters @tand 83. The wave 88 is derived from the sine wave Sd, 'and the wave 83 is derived from the sine wave 83. In normal operation, the frequency of these waves is equal, but the phase relationship between them may, and will, vary in accordance with the dark and light portions of the original subject which is being scanned by the scanner i3. The square wave of comparison voltage BB is applied across a resistor', and the square wave of voltage 39 is applied across a resistor 33. The common terminal of the resistors 92 and 33 is coupled to a control electrode 95 of a vacuum tube @l through a coupling condenser 98. A resistor` 3&3 serves as a grid resistor for the tube 3i. The resulting beat frequency voltage mi of Fig. 5 is repeated and amplified by the amplifier 9i.

This amplified voltage is applied to a full wave rectifier |02 by way of a coupling transformer -|08 and the rectified voltage |08 of Fig.6 is

. transmitter.

applied to a recorder amplier III'I across a rectifier load resistor |08.

solely by way of example and not intended as limiting the invention, *the following frequency values may be employed: The standard4 frequency source may provide a wave having, an accurately maintained frequency of 200 cycles.

The frequency multiplier Il of Fig. l2 may multiply this frequency by ten so that a 2,000 cycle wave is available for synchronizing the recorder and'for providing the constant frequency wave 84 of Fig. 3. In Fig. 1, the generator 28 may provide a frequency of 2,000 cycles in which case the frequency multiplier 39 will multiply the standard frequency output by ten. 'I'he multiplier I2 Various modifications of the system shown and described herein by way of example4 are possible,

lwithout departing from the spirit and scope of the invention described herein, and it is desired that anyr and all of such modifications be considered within the purview of the present invention defined by the hereinafter appended claims.

in this example provides a frequency of 2,000

cycles.

It will be understood that` these values may be varied and that means other than those shown may be employed for -synchronizing the equipment.l The arrangement shown in the Patent No.`

2,325,028, granted to Maurice Artzt, July 27, v1943, is suitable for the purpose. The wave t4 may be generated locally at the receiver, but, as pointed out above, this is preferably derived from the synchronizing signal which is received from the The wave |08 will record an image havingra dot pattern and therefore, where fine picture detail is desired, the waves I4 and 86 should have a high frequency.

The output from theA amplifier |01 may be modified to give 'an amplitude varying wave in the' manner disclosed and claimed in the copending application of Gordon L. Fredendall, Serial No. 488,969, filed May' 29, 1943.

- Referring to Figs. 7 to 10, a condition is shown y where a very light grey or almost white portion of the original copy is being scanned. The waves 84 and 86 in this case are almost 180 out of phase, and the resulting wave-lill shown in Fig. 10 comprises pulses of shorter time duration than the pulses exhibited by the wave HI8 of Fig. 6 under the mid-grey scanning conditions. It is believed that lthe relationship between the curves of Figs. 3 to 6 and Figs. '7 to 10 will be fully understandable without further explanation in view ofthe foregoing complete description of the invention.

Fig. 171 of the drawings shows a slightly mod` iiied -arrangement of the receiving equipment of Fig. 2 which will be employed to receive signals Having nowydescribed the invention, what is claimed and desired to be secured by Letters Patent is the following:

1. A facsimile receiving system for obtaining a record from a carrier, the phase of which is shifted in accordance with image signals, comprising means to compare the phase of said carrier from cycle to cycle with a synchronizing alternating voltage to derive another alternating voltage equal in frequency to said synchronizing voltage but having a wave form varying in accordance with the phase of said carrier, means to convert said derived alternating voltage into pulses, the time duration of which varies in accordance with the phase ofsaid carrier, a recorder having a recording element, and means quency.

from the transmitter of Fig. .1 when they device indicated by reference character 4B functions as a modulator to amplitude modulate the already phase modulated subcarrier by the synchronizing frequency from the frequency standard 33 applied over conductors 48. The signal appearing in the conductors 53 shown onl both Figs. 2 and 11 is fed directly to the limiter amplifier 82 which removes the synchronizing signal appearing as an amplitude modulation of the phase modulated carrier and shapes the phase modulated wave in a manner previouslyiexplained before it is applied to the resistor 93.

The synchronizing signal is recovered in an amplitudedetector 56a; which may be of any ,well known type, forexample, a full wave rectifier. The' output in the form of an alternating current l from the detector 56a is multiplied in the multiplier 6,8, itand the remaining Aapparatusbeing unchanged. 'I'his alternating current may be employed in the manner previously explained for synchronizing the receiver and as a reference 7 frequency. o,

A facsimile system comprising a facsimile transmitter and a facsimile recorder. means at said transmitter for transmitting'a fixed reference frequency along with image signals carried on a phase modulated subcarrier having a mean frequency integrally related to said reference frequency, means in said recorder for comparing the phase of the two frequencies and obtaining from this comparison image recording currents proportional to the phase difference, and means for synchronizing said transmitter and recorder with each other by controlling the speed of both lfrom the common reference frequency.

4. A facsimile system comprising a transmitter and a receiver, means for generating a synchronizing frequency, meansfor generating a carrierv controlled by said synchronizing frequency, means at said transmitter for generating an image signal, means for shifting the phase of said carrier in accordance with successive values of said image signal. means for utilizing said synchronizing frequency for controlling the speed of said transmitter, means for transmitting said phase modulated carrier along with said synchronizing frequency to said receiver, means at said receiver for sepa-'- rating saidv synchronizing frequency and employing it to synchronize said receiver with said transmitter, means at said receiver controlled by said synchronizing frequency for generating a fre' quency equal to the frequency of said carrier, means to .derive signals representing the phase difference between said phase modulated carrier and said locally generated frequency. means to y' rectify said derived signals, and means ,to apply said rectified signals to obtain a record 5. In facsimile apparatus wherein image signals representative of Athe optical values of a l transmitted image are received as phase modulo Y tions of a carrier and wherein a synchronizing signal is continuously received along with said carrier, means for generating `square wave signals from said received carrier, means for generating square wave signals from said synchronizing signal but equal in frequency to said carrier, means for developing a series of square Wave ypulses representative of the phase relationship means for comparing the phase of the' two frequencies of square-wave form and obtaining from this comparison image recording impulses proportional to the phase difference, means for synchronizing said recorder by controlling its speed from the reference frequency.

7. A facsimile system comprising a transmitter and a receiver, means for generating a synchronizing wave, means for generating a carrier controlled by said synchronizing wave, means at said transmitter for generating an image signal, means for shifting the phase of said carrier in accordance with successive values of said image signal, means for utilizing said synchronizing wave.for controlling the speed of said transmitter, means for transmitting said pulse modulated carrier along with said synchronizing wave to said receiver, means at said receiver for separating said y'synchronizing Wave and employing it to synchronize said receiver with said transmitter, means atsaid receiver controlled by said synchronizing vWave for generating a frequency of square wave-form equal to the frequency of said carrier, means for converting said carrier to square wave-form, means to derive impulse sig nals representing the phase difference between said phase modulated carrier of square waveform and said locally generated frequency of square Wave-form, means to rectify said derived signals, and means to apply said rectied signals to obtain a record.

8. A facsimile receiving system in which the received signals are a synchronizing signal carried n a subcarrier which is phase modulated with facsimile signals. a facsimile recorder, means for separatingl the synchronizing signal, means associated with said recorder for generating signals indicative of the speed and phase of said recorder, means for comparing the phase of said synchronizing signal and said generated signal to obtain a synchronizing voltage, and means for synchronizing said recorder by controlling its speed from the synchronizing voltage.

9. A facsimile receiving system in which the received facsimile signals appear as a phase modulation of a carrier comprising a recorder, means for obtaining a wave having a frequency equal to the frequency of the carrier and representing the desired synchronizing speed of said recorder, means for comparing the carrier and the wave which represents the synchronizing speed of said recorder, vmeans for developing square Atopped pulses representative of the comparison, and means for utilizing the pulses in said recorder to obtain reproduction of an image.

l0. A facsimile receiving system in which the facsimile signals appear as a Iphase modulation of a carrier comprising a recorder, means for obtaining a wave havinga frequency equal in frequency to the frequency of the carrier and representing the desired synchronizing speed of said recorder, means for converting said wave tov 

